Electric resistance heating units



June 4, 1963 E. J. LIMPEL ELECTRIC RESISTANCE HEATING UNITS Filed April3, 1961 3 9 I a T. L L: T1; Mn g I I I I I I I I l J I I 'I \I 1 1|INIfENTOR. 8ugene J. Llmpel BY AndrflsGSibr/p Diffarneys United StatesPatent 3,092,716 ELECTRIC RESISTANCE HEATING UNITS Eugene J. Limpel,Thiensville, Wis., assignor to O. Smith Corporation, Milwaukee, Wis., acorporation of New York Filed Apr. 3, 1961, Ser. No. 100,289 7 Claims.(Cl. 219-149) This invention relates to electric resistance heatingunits and particularly to a heating unit for heat treating steel bars,billets or the like by passing a current through the member.

Electric resistance heating units having a pair of spaced electrodeshave been employed to heat a steel billet by passing current through thebillet. The billet is clamped between the electrodes at 'least one ofwhich is movable to establish a pressure contact with the ends'of theelectrodes during the current flow.

The contact between the end of the billet and the adjacent electrodeduring the initial establishment of current flow has caused particularlydiflicult problems. The presence of an uneven end cut or any form ofprojections on the end of the billet establishes a small concentratedpoint of contact with the adjacent electrodes With a resultantexceptionally high current density through the contacting points.Burning of the-electrodes and/or the work may occur' and seriouslyaffect the efficiency and operation of the heating unit.

Various suggestions have been made. For example, it has been proposedthat an initial low density current be established to soften the roughand irregular end of the member with the applied pressure serving toflatten the member and establishing a smooth intimate contact.Thereafter,- the current is increased to provide the desired workheating ofthe member. The prior art also suggests introducing agranulated or powdered material between the adjacent end of theelectrode and the member being heated to eliminate arcing between thetwo members.

The present invention is directed to a simple and durable electrodeconstruction for producing good electrical contact with the billet orthe like.

In accordance with the present invention, the billet engaging end of thecontact or electrode is provided with a conical recess adapted toreceive the end of the billet and establish a narrow ring contact areatherewith. Current and pressure are simultaneously applied between thecontact and the billet. The initial high current density through thenarrow ring-like area immediately softens any protrusions or contactingmembers and allows the high pressure to establish firm electricalengagement in a narrow ring area. The softening of the adjacent end ofthe billet results in an increased contact area which readily and safelycarries the current density established for proper heating of the bar orbillet.

In accordance with another aspect of the present invention, the cont-actarea of the contacts is coated with or formed of a suitable hardmaterial such as carboloy, tantalum, or the like to prevent wearing awayof the contact area.

The present invention provides a simple and relatively inexpensiveelectric resistance heating contact having a long life.

The drawing furnished herewith illustrates the best mode presentlycontemplated for carrying out the invention.

In the drawing:

FIG. 1 is a side elevational view of an electric heating unitconstructed in accordance with the present invention with parts brokenaway to show details of construction; and

Patented June 4, 1963 vided for supplying power to the electrode units 2and 3 for establishing suitable current flow through the billet 1. Ahydraulic motor 7 is secured to the upper electrode unit 2 and isadapted to apply a pressure through the electrode unit 2 across thebillet 1 and establish firm electrical contact between the ends of thebillet 1 and the adjacent electrode units 2 and 3.

The illustrated steel billet 1 is provided with coined beveled edges 8to establish ring-like surfaces for initial engagement with theelectrode units 2 and 3, as subsequently described. The billet may beformed of cast or scrap steel or may be any other member adapted to beheated by passing a current through the member.

Each of the electrodes units 2 and 3 is generally similar inconstruction and the upper electrode unit is described in detail.Corresponding elements in the electrode unit 3 are correspondinglynumbered in FIG. 1 to provide similar descriptive explanation.

The electrode unit 2 includes a tubular base 9 of copper or copper alloymounted within a supporting frame structure 10 of the resistance heatingunit 4. The base'9 is supported in a suitable electrical insulatingbearing 11 to isolate the base from the frame structure 10. A coolingchamber 12 is formed within the base 9 and connected by an inlet 13 andan outlet 14 to a source of coolant such as water or the like. A contactblock 15 is brazed or otherwise intimately secured to the end of thebase 9 adjacent the billet 1.

The contact block 15 is formed of a high strength, wear resistantmaterial such as carboloy or tantalum. The outer end of the contactblock 15 is provided with a frustoconical recess 16 adapted to receivethe adjacent end of the steel billet 1 with the coined beveled edge 8engaging the wall of the recess.

The hydraulic motor 7 is connected through a suitable supporting bracket17 to the frame structure 10 and includes a piston rod 18 secured to theouter end of the electrode base 9 of the upper electrode unit 2. Thehydraulic motor 7 is adapted to axially move the electrode with respectto the billet 1 for clamping of the billet between the contact blocks15. The motor 7 establishes a relatively high pressure on the ends ofthe billet 1 engaging the wall of the respective recesses 16 of theelectrode units 2 and 3.

The power lines 5 are connected to the bases 9 of electrode units 2 and3 to establish an electrical connection through the base 9 and block 15to the billet 1.

The operation of the illustrated embodiment of the invention isdescribed as follows.

A billet 1 is inserted between the electrode units 2 and 3 and thehydraulic motor 7' operated to clamp the billet between the electrodeunits 2 and 3. The opposite ends of the billet 1 project into theadjacent recesses 16 and establish firm electrical contact between thecoined edges 8 and the corresponding surfaces of recesses 16. Thecontrol switch 6 is closed to apply current to the electrode units 2 and3 and the billet 1.

The initial current between each of the contact blocks 15 and theadjacent coined edges of the billet 1 rapidly softens the adjacentcoined edges. The motor 7, which is a very rapid response motor, quicklymoves the upper electrode unit 2 to maintain a pressure engagementbetween the electrode contact blocks 15 and the ends of the billet 1 andremoves any uneveness which may have occurred as a result of the coiningor the like. Any slight arcing which may occur does not adversely affectthe adjacent wear resistant carboloy blocks 15.

The heat applied across the narrow contact area or band as a result ofthe concentrated current in the band continues to soften the adjacentedge portion of the billet 1 and the softened edge of the billet 1 iscompressed and displaced with a continuously increasing contact area,such as shown in phantom in FIG. 1.

Although the contact blocks 15 are shown as separate solid blocks brazedor otherwise secured to the base 9, the wear resistant surfaces can beprovided in any other suitable manner. For example, the base 9 can beextended and provided with suitable conical recesses for receiving theend of the billet. A carboloy or other hard, wear resistant material canbe sprayed, evaporated or otherwise applied to the contact area toprovide a longlife contact.

The present invention thus provides an improved electric resistanceheating electrode having a highly Wear resistant contact face and animproved contact with the member being heated.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim: 1

1. In a contact in a heat treating unit for resistance heating of abillet having the edges beveled to produce a ring contact area withoutsubstantial deformation thereof, a contact base, and a contact block ofwear resistant material intimately attached to the contact base, saidblock having a recess with tapered walls and with an opening diametergreater than the end of the billet and a final diameter less than thebillet to define a contact area receiving the beveled edge of the billetand establishing an initial narrow ring contact with the billet.

2. In a contact in a heat treating unit for resistance heating of abillet having coined beveled edges without substantial deformationthereof, a cont act base, and a contact block of carboloy attached tothe contact base, said block having a recess with tapered walls and withan opening diameter greater than the end of the billet and a finaldiameter less. than the billet to define a contact area receiving theend of the billet and establishing an initial narrow ring contact withthe billet.

3. The method of resistance heating for heat treating of a steel billet,comprising the steps of coining the end edges of the steel billet,securing the billet between a pair of electrodes having tapered openingsreceiving the ends of the billet, applying pressure to at least one ofthe elec trodes, applying power to the electrodes to heat the billet,and said pressure establishing a ring-like contact area withoutsubstantial deformation of the billet while maintaining firm electricalengagement therebetween.

4. In a contact unit in a heat treating unit for resistance heating of aworkpiece having a planar end without ubstantial deformation thereof, anelectrode including a contact end having a recess with tapered sidewalls for receiving the end of the workpiece and engaging the outer edgeof said end, and control means adapted to establish limited relativemovement of the workpiece and the contact end for establishing limiteddeformation of the outer edge of the workpiece engaging the contact endand thereby establishing an initial narrow ring contact with theworkpiece.

5. The contact unit of claim 4 having cooling means associated with thecontact end to cool the tapered side walls.

6. The contact unit of claim 4 wherein said recess is a frusto-conicalrecess.

7. The contact unit of claim 6 wherein said recess includes a carboloycontact surface.

References Cited in the file of this patent UNITED STATES PATENTS1,731,858 Grist Oct. 15, 1929 1,756,857 Gilson Apr. 29, 1930 2,178,032Clausen Oct. 31, 1939 2,890,324 Havlik June 9, 1959

1. IN A CONTACT IN A HEAT TREATING UNIT FOR RESISTANCE HEATING OF ABILLET HAVING THE EDGES BEVELED TO PRODUCE A RING CONTACT AREA WITHOUTSUBSTANTIAL DEFORMATION THEREOF, A CONTACT BASE, AND A CONTACT BLOCK OFWEAR RESISTANT MATERIAL INTIMATELY ATTACHED TO THE CONTACT BASE, SAIDBLOCK HAVING A RECESS WITH TAPERED WALLS AND WITH AN OPENING DIAMETERGREATER THAN THE END OF THE BILLET AND A FINAL DIAMETER LESS THAN THEBILLET TO DEFINE A CONTACT AREA RECEIVING THE BEVELED EDGE OF THE BILLETAND ESTABLISHING AN INITIAL NARROW RING CONTACT WITH THE BILLET.